The present invention relates generally to magnetic storage apparatus and, more particularly, to high-density magnetic storage devices having the recording density of more than 4 gigabits per square inch (Gbit/in2). The invention also relates to magnetic recording media of low noise and high reliability with reduced reproduction output attenuation occurring due to thermomagnetic relaxation to attain high-density recordabilities required.
In recent years, as magnetic storage apparatus rapidly increases in recording density, it is demanded to attain high-sensitivity magnetic heads along with advanced magnetic storage media high in magnetic coercive force and yet low in noise. While currently available magnetic head assemblies typically employ a magnetic head of the magnetoresistance effect type, also known as magnetoresistive (MR) heads, an endless demand for increased data storage density calls for accelerated development of further advanced magnetic heads of the giant magnetoresistance (GMR) type which are two or three times greater in sensitivity than standard MR heads.
In addition, as portable or handheld personal computers (PCs) such as xe2x80x9cnotebookxe2x80x9d PCs are sharing larger part in the digital computer market, prior known storage media with an Alxe2x80x94Mg alloy substrate metallized or plated with NiP (referred to as xe2x80x9cAl substratexe2x80x9d hereinafter) are being replaced with glass-substrate media having enhanced physical durability or robustness against attendant shocks during hand-carrying or xe2x80x9con-the-flyxe2x80x9d usage outside the users"" offices, which media are under accelerated development today. Unfortunately, advantages of such glass-substrate media do not come without accompanying a penalty: these tend to decrease in magnetic properties more significantly than conventional Al-substrate media due to defective adherence, immersion or xe2x80x9cinvasionxe2x80x9d of impurity gasses from a substrate into its associative films, degradation of in-plane orientation of magnetization easy axis, increased particle or grain sizes, and others. An approach to avoiding such problem associated with the prior art is to newly form between the substrate and an undercoat layer or underlayer more than one additive layer including an intermediate layer, seed layer, barrier layer and the like. One typical scheme incorporating this principle has been disclosed in, for example, JP-A-1-134913 (laid open on May 26, 1989). A similar scheme is set forth in JP-A-1-134984 (laid open on May 26, 1989). These Japanese documents teach and suggest that the adhesiveness might increase by formation of an intermediate layer which is made of oxide of a chosen metal containing therein at least one element as selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Mn, which leads to achievability of good contact-start-stop (CSS) characteristics. In addition, referring to JP-A-4-153910 (laid open on May 27, 1992), it is disclosed therein that formation of an amorphous or micro-crystalline film may enable miniaturization of particle or grain dimensions to thereby reduce the risk of attendant noises, which film is comprised of Y as well as one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W. JP-A-5-135343 (laid open on Jun. 1, 1993) demonstrates the fact that forming on a glass substrate an oxygen isolator layer allows resultant magnetic coercive force to increase, which layer contains therein a chosen rare earth element in addition to one kind of element selected from the group consisting of Ta, Y, Nb and Hf. Reference is further made to JP-A-7-73441 (laid open on Mar. 17, 1995), which indicates obtainability of higher coercive force by forming on a substrate either an amorphous Cr alloy or V alloy because such formation permits a Cr under-layer formed thereon to exhibit the (211) orientation causing a Co-alloy magnetic layer to have the (10.0) orientation with its magnetization easy axis facing the inside of a film surface, i.e. lying parallel to the film surface.
A layer as directly formed on a substrate for purposes of grain size control and impurity invasion elimination and so on will consistently be referred to as the first underlayer, whereas another underlayer with the body-centered cubic (xe2x80x9cbccxe2x80x9d) structure made of a Cr alloy or any equivalents thereto for orientation control of a magnetic epitaxial-growth layer will be as the second underlayer in the description below.
Also note that while medium noise reduction calls for miniaturization or microfabrication of magnetic particle or grain diameters along with reduction of interaction between grains for interchanging, resultant recording magnetization can decrease or attenuate with time due to the fact that miniaturized or xe2x80x9cshrankxe2x80x9d magnetic crystals would be affectable from thermal disturbance more significantly. This is called the xe2x80x9cthermomagnetic relaxation,xe2x80x9d which will become significant with an increase in recording density. In light of the foregoing, in order to achieve ultrahigh recording density, it should be required to suppress or minimize any possible thermomagnetic relaxation while at the same time letting noise reduction be obtainable.
It is therefore an object of the present invention to provide an improved magnetic storage apparatus and a magnetic recording medium adaptable for use therewith.
It is another object of the invention to provide a high-density magnetic recording medium of low noise with enhanced stability against thermomagnetic relaxation as achievable through appropriate control of the crystal orientation and average grain dimension as well as grain size distribution in more than one magnetic layer used therein.
It is a further object of the invention to provide a magnetic storage apparatus high in reliability having an increased recording density of more than 4 gigabits per square inch as attainable by use of a high-sensitivity magnetic head in combination with the magnetic recording medium.
In accordance with one aspect of the instant invention, a magnetic storage apparatus is provided which includes: a magnetic recording medium having a magnetic layer formed on a substrate with a single or multiple underlayers laid between them and featured in that at least one of the underlayers is made of an amorphous or microcrystalline material which contains therein Ni as its main component and also contains at least one kind of element selected from the group consisting of Nb and Ta; a drive unit for driving the record medium in the recording direction; a magnetic head assembly consisting essentially of a recorder section and reproduction section; means for forcing the magnetic head assembly to relatively move with respect to the magnetic record medium; and, record/playback signal processor means for handling signal inputting toward the magnetic head and for performing reproduction of an output signal from the magnetic head, wherein the reproduction section of said magnetic head is configured from a magnetoresistive (MR) head.
In accordance with another aspect of the invention, a magnetic storage apparatus is provided including: a magnetic recording medium having a magnetic layer formed on a substrate with a single or multiple underlayers sandwiched therebetween, at least one of which layers is comprised of an amorphous or microcrystalline material containing as its principal component at least one kind of element selected from the group consisting of Nb, Zr, Ta, and Mo and also containing Si therein; a drive unit for driving the record medium in the recording direction; a magnetic head assembly formed from a recorder section and reproduction section; means for forcing the magnetic head assembly to move relative to the magnetic record medium; and record/playback signal processor means for handling signal inputting to the magnetic head and for performing reproduction of an output signal from the magnetic head, wherein the reproduction section of said magnetic head is structured from an MR head.
Use of an amorphous or microcrystalline material containing Si mentioned above as the first underlayer serves advantageously to permit miniaturization of crystal grains in the second underlayer and magnetic layer, and may also offer an effect of reducing grain size distribution to thereby uniformalize the resultant grain diameter. This may in turn suppress distribution of magnetization inversion magnetic fields, thereby enabling achievement of higher magnetic coercive squareness along with enhanced overwritability. A further advantage lies in that a reduction in playback output occurring due to thermal fluctuation may be suppressed even when the average grain size is reduced. This can be said because the grain size uniformalization permits removal of extra-fine magnetic crystal grains or particles that remain much affectable from thermal fluctuation. Preferably, the Si addition amount is greater than or equal to 5 atomic-percent (at %) and yet less than, or equal to, 35 at %. Setting the Si amount out of this range is not recommendable because if the Si addition amount is less than 5 at % or greater than 35 at % then crystallization can take place or alternatively the xe2x80x9cfattingxe2x80x9d of crystal occurs undesirably. Especially, when the Si addition amount is set in a range of from 10 to 20 at %, resultant crystal grains are successfully downsized or miniaturized enabling achievement of extra-low noise media.
Note here that the term xe2x80x9camorphousxe2x80x9d as used herein may refer in nature to a state in which no clear peak is observed by X-ray diffraction, or alternatively, halo diffraction rings are observed but not any crisp diffraction spots and clear diffraction rings by electron diffraction. In addition, the term xe2x80x9cmicrocrystallinexe2x80x9d as used herein refers to those crystals that are less in grain size than an associated magnetic layer(s)xe2x80x94preferably, the average size is 8 nanometers (nm) or less.
Use of an amorphous or microcrystalline material which contains therein Ni as its main component mentioned above as the first underlayer also enables miniaturization and uniformalization of magnetic layer crystal grains, which in turn makes it possible to obtain an intended storage medium of low noise while suppressing playback output reduction occurring due to thermomagnetic relaxation. It is preferable that the addition amount of Nb be in a range of from 20 to 70 at % whereas Ta ranges from 30 to 60 at % in addition amount. Otherwise, either crystallization of the underlayer or fatting of crystal grains will occur undesirably. The magnetic layer may be further improved in miniaturization and uniformity of crystal grains when additionally doping thereinto a prespecified oxide of at least one kind of element selected from the group consisting of Al2O3, SiO2, TiO2, ZrO2 and Ta2O5, which leads to achievability of media with further enhanced noise reduction. This is because of the fact that the phase of such added oxide remains uniform in deposition within Ni-alloys of its matrix phase, thereby permitting precise and uniform fabrication of crystal grains while letting them behave as nucleation cites. Additionally, the second underlayer of Cr or containing Cr as its main component that was formed on said first underlayer to have the body-centered cubic (bcc) structure exhibits the (100) orientation. Hence, the magnetic layer formed thereon with hexagonal closest (hcp) structure has the (11.0) orientation with its c-axisxe2x80x94namely magnetization easy axisxe2x80x94being essentially directed parallel to the film surface due to epitaxial growth. This enables achievement of increased magnetic coercive force and improved coercive squareness S* thus making it possible to attain high recording densities of 4 gigabits per square inch (Gbit/in2)or more. The first underlayer of the invention is further featured in significance of the adhesiveness with glass substrates; especially, this may avoid a need to provide any extra layer used for improvement of adhesion. However, it will also be able to form a pattern of uneven configuration on a medium and then fabricate between the substrate and first underlayer a certain layer for improvement of the CSS characteristics, which may be either a continuous layer or a discontinuous layer with an ensemble of islands grown. Furthermore, the substrate may be a NiP-metallized Al-alloy substrate or alternatively an amorphous carbon substrate; in this case also, similar miniaturization and uniformalization of crystal grains in the magnetic layer have been affirmed as in the case of the glass substrate, which results in accomplishment of medium noise reduction while attaining suppressibility of thermomagnetic relaxation.
The second underlayer that is formed on the first underlayer for orientation control of the epitaxial-growth magnetic layer may be made of an alloy of the bcc structure which is of pure Cr or contains Cr as its principal component and which further contains therein Ti, V, Mo or the like. Optionally, the second underlayer may be formed from a lamination of two or more layers each having the bcc structure.
Although an alloy of the hcp structure with Co being as its main component is employable for the magnetic layer, it is preferable in order to obtain higher coercive force that the magnetic layer be made of a Co alloy containing Pt therein. It will also be acceptable to employ magnetic alloys containing a rare earth metal element or elements with high magneto crystalline anisotropy, including but not limited to SmCo or FeSmN. It is further noted that the magnetic layer could be formed from a single-layer or multiple layers with a nonmagnetic intermediate layer being sandwiched between adjacent ones of them; in the latter case, the thickness t of such magnetic layer in xe2x80x9cBrxc3x97txe2x80x9d product as described below is defined to equal to the total sum of thicknesses of respective magnetic layers used. In regard to magnetic characteristics of the magnetic layer, the coercive force as measured upon application of a magnetic field in the recording direction is preferably set at 2 kilo-oersteds (kOe) or greater whereas a product Brxc3x97t of the residual magnetic flux density Br and film thickness t is designed so that it falls within a range of 40 to 120 Gauss-microns. With such value settings, it will become expectable to attain superior recording/reproduction (read/write) characteristics in those regions of recording densities of more than 4 Gbit/in2. If otherwise the coercive force is below 2,000 Oe then an output undesirably decreases at high recording density (200 kFCI or more). If the value Brxc3x97t goes beyond 120 Gauss-microns then the resolution can decrease; if below 40 Gauss-microns then resultant playback output will be lowered undesirably. Especially, coercive force more than 2,400 Oe is preferable in order to obtain further low media noise at high linear density.
Further, by forming as a protective layer of the magnetic layer a carbon film of 5 nm to 30 nm thick and then providing thereon a lubrication layer with absorbabilities, such as perfluoroalkylpolyether or other suitable similar materials, to a thickness of 2 to 20 nm, it becomes possible to obtain a high-density magnetic recording medium with high reliability. Preferably, the protective layer may be a carbon film with hydrogen or nitride added thereto, or a film comprising a compound of silicon carbide, tungsten carbide, (Wxe2x80x94Mo)xe2x80x94C, (Zrxe2x80x94Nb)xe2x80x94N and the like, or alternatively a mixture film of such compounds and carbon, which in turn makes it possible to successfully improve the resistance to sliding movements and the anticorrosion property.
It will also be preferable that in the MR head assembly for use with the magnetic recording apparatus stated supra, two shield layers with the MR sensor unit sandwiched between them be less than or equal to 0.30 xcexcm in distance (shield distance). This can be said because if the shield distance goes beyond 0.30 xcexcm then the resolution can decrease causing resultant signals to increase in phase jitter. A further advantage of the invention is that it is possible to further enhance the magnitude of net signals and thus achieve high-reliability magnetic storage apparatus with increased recording density of more than 5 Gbit/in2, by letting the MR head assembly employ an MR sensor that includes multiple conductive magnetic layers each capable of generating a significant resistivity change in response to a relative change in mutual magnetization directions in the presence of an external magnetic field applied thereto, and more than one conductive nonmagnetic layer as disposed between such conductive magnetic layers to thereby utilize either the giant magnetoresistance (GMR) effect or the spin valve effect.